Abstract
Dark-operative protochlorophyllide (Pchlide) oxidoreductase (DPOR) catalyzes the stereo-specific reduction of C17-C18 double bond to form chlorophyllide a (Chlide) in the (baterio)chlorophyll biosynthesis. DPOR consists of two separable components, L-protein (BchL dimer) as a reductase component and NB-protein (BchN-BchB heterotetramer) as a catalytic component, which are functional counterparts of Fe protein and MoFe protein of nitrogenase, respectively. Even though the requirement of ATP for DPOR reaction has been demonstrated, it is still unknown how many ATP molecules are hydrolyzed upon Chlide formation. Here we report a stoichiometric analysis of DPOR from Rhodobacter capsulatus. The observed ATP:Chlide (2e- equivalent) ratio increased in a linear way with increase in the ratio of L-protein to NB-protein (L/NB ratio). The minimum value of ATP/2e- ratio of 4 was obtained by extrapolation, which is coincident with that of nitrogenase. This result suggested that the ATP-dependent electron transfer mechanism is common between DPOR and nitrogenase.
